Radiation therapy for the prostate and individual metastases in metastatic prostate cancer

Prostate cancer usually originates in the glandular cells of the prostate; this most common form is called adenocarcinoma. In some patients, the cancer has already spread (metastasized) by the time of diagnosis. In prostate cancer, these metastases most commonly occur in the bones. A key pillar of treatment is anti-hormone therapy. The male sex hormone testosterone is an androgen and can promote the growth of prostate cancer cells. Therefore, its production or effects are suppressed with medication. In the study, patients continue to receive combined anti-hormone therapy consisting of hormone deprivation (ADT) and a drug that blocks the androgen receptor signaling pathway (ARPI). The PSA (prostate-specific antigen) level is a protein that can be measured in the blood. Its level can provide indications of prostate cancer activity. If the PSA level remains above 0.2 ng/ml after six months of anti-hormone therapy, this suggests that the disease has not been completely suppressed. For these patients, the study is investigating an additional localized treatment: radiation therapy to the prostate and to any metastases that still appear active on imaging (PSMA-PET/CT). Radiation therapy uses high-energy radiation to damage cancer cells in the irradiated area. PSMA-PET/CT is an imaging technique that can visualize prostate cancer cells based on a characteristic surface marker (the prostate-specific membrane antigen, PSMA). This allows for targeted irradiation of the affected areas rather than the entire region.

The aim of this study is to investigate whether additional radiation therapy to the prostate and the still-active metastases after six months of anti-hormone therapy can lead to a measurable reduction in the disease as seen on imaging. The study is uncontrolled (there is no comparison group) and open-label (not blinded), meaning that both the patients and the study physicians know which treatment is being administered. During the study, patients will undergo three PSMA-PET/CT scans and visit the clinic every three months for 3 years. PET scans are scheduled before radiation therapy and one year afterward. At each visit, patients will complete questionnaires on quality of life.

Eligible participants are patients aged 18 to 85 with prostate adenocarcinoma that had already metastasized at the time of initial diagnosis (at least four bone metastases, possibly with lymph node metastases, but without metastases in internal organs). Eligibility requires six months of combined anti-hormone therapy, followed by a PSA level that remains elevated above 0.2 ng/ml, as well as fewer than 16 bone or lymph node metastases on PSMA-PET/CT.